Experiments will be performed on dissociated sympathetic neurons from the superior cervical ganglion of the newborn rat 1) to investigate further the character of synapses they have been found to form with each other in tissue culture, 2) to determine the conditions under which the neurons will form junctions with cardiac and smooth muscle cells in quasi-monolayers, and 3) to study the properties of the junctions as they develop. The work will be collaborative, involving electrophysiological, electromicroscopical, histochemical and biochemical techniques. Microelectrode techniques will be used to determine whether particular neurons have formed effective junctions and to investigate the character of the junctions, i.e. whether they are excitatory or inhibitory, adrenergic or cholinergic, and of what receptor type. These same identified neurons will then be examined by electronmicroscopical or histochemical methods to learn more about the nature and degree of development of the junctions. Cultures grown in the same way will be examined with biochemical methods to determine the ability of the neurons to synthesize, store and release catecholamines and acetylcholine.